Device for the variable control of the valves of internal combustion engines, more particularly for the throttle-free load control of 4-stroke engines

ABSTRACT

The invention relates to a possibility for the relative rotation of two camshafts for the control of internal combustion engines, more particularly to reduce the gas exchange losses of reciprocating 4-stroke engines. The invention more particularly enables very large adjustment angles of up to 220° crank angle to be obtained.

BACKGROUND OF THE INVENTION

The invention relates to a device for the variable control of the valvesof internal combustion engines, more particularly for the throttle-freeload control of 4-stroke engines via the intake stroke functions of oneor more intake valves per cylinder. Two camshafts rotate to oppositehands and act via a transmission member, more particularly a rockinglever on the or each valve spring-loaded in the closure direction, onecamshaft determining the opening function and the second camshaft theclosing function, so that the stroke and/or duration of opening of theor each valve can be changed in relation to one another over wide rangesby a relative rotation of the two camshafts.

Such a valve control system is known from Offenlegungsschrift DE-OS 3531 000. In that valve drive the required variability of a valve controlsystem, principally to avoid throttle losses, is effected by the featurethat the opening and closure operation is performed by two differentcontrol cams running at a controllable phase angle to the crankshaft. Acontrol lever of any desired construction is so actuated by the twocamshafts that the valve spring-loaded in the closure direction isopened only when both control cams are extended. In this way variablevalve control times can be adjusted by a suitable phase position of thecamshafts. A similar valve control system for intake valves ofreciprocating piston internal combustion engines is disclosed in DE-OS35 19 319 to which U.S. Pat. No. 4,714,057 corresponds. In that case, inaddition to a rotating stroke camshaft, a control camshaft rotating atthe same speed engages at a displaceable bearing place of the pivotablevalve lever. In principle variable valve control systems can be obtainedin this way, wherein the course of the valve stroke can be so altered asto reduce the gas exchange losses caused in 4-stroke engines bythrottling.

In the system disclosed in DE-OS 35 31 000 the relative rotation of thetwo camshafts takes place via accelerator-controlled camshaft drivingwheels, which can be displaced on corresponding steep threads. Onlysmall angles of rotation with relatively long adjustment times are alsopermitted by the camshaft phase adjusters, known from other PatentSpecifications and Offenlegungsschriften (e.g., DE-OS 29 09 803), someof which are already in serial production, which operate on theprinciple of the axial displacement of a piston on a helical groove.Moreover, the prior art systems occupy a large constructional space,more particularly in the direction of the engine longitudinal axis.

To achieve throttle-free load control over the whole operating range ofpresent-day motor vehicle 4-stroke engines, relative angles of rotationbetween the two camshafts of an order of magnitude of 150° to 220°crankshaft are required, if the intention is also to use the potentialof optimum valve control times for maximum filling under full load overthe whole speed range. Moreover, due to the demands of dynamic vehicleoperation, the adjusting process must take place within very shortperiods of time (fractions of seconds). The adjuster itself should be ofcompact construction, to meet present-day spatial conditions in theengine chamber.

DE-PS 470 032 discloses a valve control system for internal combustionengines which is mainly characterized in that to control the valve twonon-circular control discs are provided whose axes of rotation alwaysmaintain their position in relation to the axis of rotation of atransmission lever. The valve-actuating transmission lever takes theform of a two-part rocking lever which has a fixed pivot and which, whenthe two plate cams rotate in relation to one another, cancorrespondingly change within narrow limits only the duration of openingor closing of the valves, but not the valve stroke. It is a so-called ORcircuit wherein the valve stroke is always determined by the controldisc having the maximum operative stroke circle. To avoid jumpyfunctioning with consequent impermissibly high accelerations in valveoperation when the two control discs rotate in relation to one another,a transition from one control disc to the other can in fact only be madewith a constant operative stroke, essentially with the maximum stroke.As a result, the usable adjustment range of that system is heavilylimited and unsuitable for throttle-free load control. The epicyclicgear for driving a control disc as disclosed in this citation is at thesame time used to rotate the two control discs in relation to oneanother. The epicyclic gear consists of four toothed wheels, of whichtwo toothed wheels are disposed on the parallel shafts of the twocontrol discs and are driven via two further serially connectedintermediate wheels. The two intermediate wheels are borne by a movablearrangement of links which gives them an epicyclic motion. Thearrangement of links consists of three individual links, of which twolinks each connect a toothed wheel disposed on the shafts of the controldiscs to an intermediate wheel, while the third link interconnects thetwo first-mentioned links. The two links are however not connected tothe pivots of the two intermediate wheels, but at some distancetherefrom. However, this arrangement of the third link permits anadjustment of the epicyclic gear only when the links bearing theintermediate wheels, the third link and a plane lying in the axes ofrotation of the two control discs are disposed parallel with oneanother. The arrangement of the links of the epicyclic gear must inpractice have the shape of a parallelogram, since only in that case dothe distances of the two opposite links remain identical for everyposition of the arrangement of links, something which for this kind ofarrangement of links is the basic precondition for the satisfactoryfunctioning of the meshing gear wheels. As a result, of course, thediameters of the four engaging gear wheels are directly dependent on oneanother, the transmission ratios between the toothed wheels disposed onthe shafts of the control discs and the intermediate wheels beingpredetermined within close limits. More particularly, the diameters ofthe toothed wheels cannot be freely selected to influence thesensitivity of the angle of rotation of the control shaft to be rotated.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a 4-wheel coupled gear forthe variable control of the valves of internal combustion engines which,with an inexpensive construction and small overall size, so preventschanges of contact occurring in all the toothed wheels of the coupledgear that toothed wheel rattle and damage to the pairs of toothed wheelsof the coupled drive are obviated.

According to the invention, the driving and driven shafts of the coupledgear are interconnected via an additional gear with a wheel pairinghaving different operative diameters and at least one frictionalconnection in the gear, so that a drag force is generated which issuperposed on the alternating forces transmitted by the valve drive.

The different operative diameter of the additional wheel pairing inrelation to the operative diameter of the wheels of the coupled geargenerates in cooperation with the frictional connection essential to theinvention a drag force which reliably prevents changes of contact andthe problems arising therefrom.

Preferably a device according to the invention is intended to providethrottle-free load control in 4-stroke engines throughout the wholeoperating range. The preconditions for this are in the first place metby the feature that the valve stroke, more particularly of the inletvalves, can be steplessly adjusted from zero stroke to maximum strokewith adequate variability of the closure control times. The deviceprovided for this purpose operates after the fashion of an incrementalgear, wherein the valves spring-loaded in the closure direction areopened only when two camshafts rotating at the same speed engage bytheir stroke functions via the associated pickup elements of atransmission member, more particularly a lever. One camshaft determinesthe opening function of the valve, while the other camshaft determinesits closure function. The stroke and/or duration of opening of thevalves can be changed over wide ranges by rotating the two camshaftsconcerned in relation to one another.

For this purpose the two camshafts engage with one another according tothe invention via a 4-wheel coupled gear, one wheel of the coupled gearbeing rigidly connected to the first camshaft driven by the crankshaftand via the two intermediate wheels driving the driven wheel andtherefore the second camshaft. In contrast with DE-PS 470 032, however,the wheels of the gear are each borne in their pivots by the couplers,thus creating additional degrees of freedom in the geometric layout ofthe gear. The individual couplers are constructed in the form of simplebowed members in one or more parts, the first coupler being preferablyrotatably mounted by one end on the driving camshaft and bearing by itsother end a shaft on which the first intermediate wheel and the secondcoupler are borne. The second coupler, which can also be constructed inthe form of a simple bowed member, so interconnects the two shafts,acting as pivots, of the first and second intermediate wheel that bothwheels can mutually drive one another. Again, the third coupler has atone of its ends the pivot of the second intermediate wheel while by itsother end it is so pivotably mounted and suspended on the secondcamshaft that the second intermediate wheel drives the driven wheel,also disposed on said camshaft, of the coupled gear. When the couplersare adjusted by rotation around the pivots of the rigidlycasing-attached camshafts, due to the principle of the construction alarge angle of rotation of the driven camshaft in relation to thedriving camshaft is set up by the fact that the angle of rotation of thecrank gear is superposed by the rolling-down on one another of the gearwheels of the coupled gear. To accommodate this adjusting mechanism, thecylinder head need be lengthened by only approximately the required spurgear wheel width, without any additional axial constructional spacebeing required for the adjusting path itself. Due to the superposing ofthe adjusting path of the coupler and the rolling-down of the gearwheels on one another, the adjusting path transversely of the enginelongitudinal axis is very small. Moreover, due to the small adjustingpaths of the coupled gear, adjustment can be performed in a problem-freemanner within the necessary short times, using suitable actuators.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a diagrammatic view of the adjusting mechanism according to theinvention,

FIG. 2 an illustration of the principle of a twin-camshaft valve drivefor the variable control of disc valves as set forth in the preamble ofthe Application,

FIG. 3 a diagrammatic illustration of the adjusting mechanism withoverlapping gear wheels,

FIG. 4 a possible way of clamping the adjusting mechanism,

FIG. 5 a diagrammatic illustration of an additional phase adjuster incombination with the adjusting mechanism according to the invention, and

FIGS. 6-11 different combinations for driving the camshafts of a triplecamshaft engine from the crankshaft and the arrangement of the coupledgear according to the invention.

FIG. 12 is a partial section illustrating a drag mechanism forpreventing change of contact in the coupled gear teeth.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An adjusting mechanism shown basically in FIG. 1 and taking the form ofa coupled gear (5) is a combination of a four-member crank gearcomprising three rotatably interconnected couplers (10), (11) and (12)having two rigidly casing-attached pivots (P1) and (P2), and a wheelgear whose four serially connected and mutually driving gear wheels (6),(8), (9) and (7) are mounted on the pivots (P1), (P3), (P4) and (P2) ofthe crank gear. Preferably the 4-wheel gear takes the form of a toothedwheel gear. The driving wheel (6) is rigidly connected to first camshaft(1) of the known device for variable control, driven by the crankshaft,and drives the intermediate wheel (8) borne by the first coupler (10).The intermediate wheel (8) is connected via a second coupler (11) to afurther intermediate wheel (9), which it drives. Via coupler (12) theintermediate wheel (9) is suspended on a driven wheel (7) attached tothe second camshaft (2) of the valve drive, so that by this meansfinally the second camshaft is driven to the opposite hand from thefirst camshaft. The requirement for the two camshafts to have the samespeed means that at least the driving wheel (6) and the driven wheel (7)rigidly connected to the camshafts have the same operative diameter.

When, for example, the coupler (10) rotates around the rigidlycasing-connected pivot (P1) which can advantageously coincide with theaxis of rotation of the driving camshaft, the driven wheel (7) and thesecond camshaft (2) rigidly connected thereto (FIG. 2) are rotated inrelation to the first camshaft (1) (FIG. 2) by the superposed movementof the crank gear and the rolling-down of the wheels of the wheel gearon one another. In the first place it is immaterial for the adjustmentitself at what place of the coupled gear the adjusting operation isinitiated. Since the intermediate wheels (8) and (9) are guided in thepivots (P3) and (P4) of the three couplers, the distance of the fourengaging gear wheels remains unchanged in all positions of the couplers,even if the crank gear, as shown in FIG. 1, does not take the form of aparallelogram. As a result, additional degrees of freedom are opened upin the design of the gear, more particularly as regards the diameters ofthe gear wheels, the distance between the driving camshaft and thecamshaft to be driven and, in dependence thereon, the lengths andpositions of the couplers in relation to one another.

FIG. 2 shows diagrammatically a twin camshaft valve drive in whichcontrol times can be obtained with disc valves by means of the adjustingmechanism according to the invention. The device consists of twocamshafts (1, 2) which rotate at the same speed and whose cams act viasuitably shaped pickup members on a rocking lever (3). The rocking lever(3) transmits its motion to a conventionally constructed valve (4)spring-loaded in the closure direction. Due to the superposed course ofmotion of the rocking lever (3) it cannot be mounted directly on arigidly casing-attached pivot, but must be guided by other suitablesteps. As shown in FIG. 2, it is guided, by way of example, via anarticulated lever (37) which, as shown in this instance, is articulatedto the rocking lever (3) by one end at the central point of a pickupmember following the camshaft (1), being pivotably mounted by its otherend in the centre of the camshaft (2). This system operates by aso-called AND connection. The valves are opened only when both camshafts(1, 2) act by their stroke functions on the rocking lever (3). To makethings clearer, the course of motion will now be described for anyrequired configuration and a course of valve stroke:

Let it be assumed by way of example that as shown in FIG. 2 the camshaft(1) is the opening shaft rotating clockwise and the camshaft (2) is theclosure shaft rotating anticlockwise. The two camshafts each haveprofiles made up by base circles (38, 39), stroke circles (44, 45) andascending cam flanks (40, 42) and descending cam flanks (41, 43). Theoperation starts by the camshaft (2) acting by its stroke circle (45) onthe rocking lever (3), without the valve (4) opening, as long as thecamshaft (1) is still acting by its base circle (38) on the rockinglever (3). Only when the camshaft (1) contacts the rocking lever (3) byits stroke flank (40) does the valve (4) begin to open. Then, as soon asthe camshaft (2) acts by its descending flank (43) on the rocking lever(3), a superposed rotary movement of the rocking lever, now mainlyoperating as a tipping lever, starts around the momentary point ofcontact with the camshaft (9), such movement initiating the closureoperation of the valve (4). The valve is completely closed when thecamshaft (2) again acts by its base circle (39) on the rocking lever(3). The following transition of the camshaft (1) from the stroke circle(44) to the base circle (38) is insignificant for the course of valveopening. The course of the valve stroke can therefore be continuouslyadjusted from zero stroke up to extremely long durations of operationwith maximum stroke by the stepless rotation of the camshaft (2) inrelation to the camshaft (1). At the same time, the smallest valvestrokes with very short durations of opening can be adjusted by thecamshaft (2) being so rotated by means of the aforedescribed coupledgear (5) in relation to the camshaft (1) and correspondingly to itsdirection of rotation that, as the camshaft (1) is starting to open thevalve (4) by its ascending flank (4), the camshaft (2) already completesthe superposed closure process by its descending flank (43). In verylong durations of valve opening with maximum stroke, the camshaft (2)must be so far adjusted contrary to its direction of rotation that thecamshaft (2) initiates the closure process by its transition from thestroke circle (45) to the descending flank (43) only after the openingcamshaft (1) acts by its stroke circle (44) on the rocking lever (3), sothat the valve (4) is completely opened. With the coupled gear accordingto the invention an adjustment range of 150° to 220° crank angle,appropriately usable with this valve operation, can be advantageouslyobtained with comparatively small adjustment paths. Of course, thiscoupled gear can also be used for the solution of other comparableproblems, in which a first shaft is to be driven to the opposite handfrom a second shaft and rotated in relation thereto.

The coupled gear (5) can be disposed with its driving wheel (6) anddriven wheel (7) directly on the camshafts (1) and (2) of the previouslydescribed variable valve drive, and the direction of rotation of thecamshafts and the association as regards the opening and closurefunctions can be determined as desired. Since preferably the twocamshafts are provided to actuate the intake or exhaust valves of atop-scavenged internal combustion engine, at least one additionalcontrol shaft must be provided for controlling any other valves notactuated by the aforedescribed variable valve control system. The resultis various possible combinations, shown by way of example in FIGS. 6, 7and 8, for the driving of in that case at least three camshafts by thecrankshaft and the arrangement of the coupled gear. FIG. 6, showscorresponding to FIG. 2 a combination in which a third shaft (32),usually the exhaust camshaft, not responsible for the variablycontrollable valves, is driven by crankshaft (33) via a suitabletransmission element (34), for example, a toothed belt or a chain. Viaan intermediate drive (35), which can also take the form of a toothedbelt or chain drive or a toothed wheel gear, the camshaft (32) drivesthat camshaft (1) of the variable valve drive which is not to berotated. In that case the camshaft (2) is driven and adjusted by meansof the aforedescribed coupled gear (5). As shown in FIG. 7, the camshaft(1) of the variable valve drive is directly driven via a correspondingdrive (34) by the crankshaft (33) and itself drives a third camshaft(32) via a transmission element (35) and via the camshaft (2) to theopposite hand via coupled gear (5). FIG 8 shows a possible way ofabandoning any extra intermediate drive and driving the two controlshafts (1) and (32) not to be rotated by means of a common driving means(36). In the aforedescribed possibilities for the driving of thecamshafts by the crankshaft, the driving means and also the coupled gearaccording to the invention can each in accordance with marginalconditions be disposed as desired at the two end faces of the engineand/or at a suitable place inside the engine constructional space.

In accordance with FIGS. 9-11 it may be convenient for the driving wheel(6) of the coupled gear (5) to be disposed on a third shaft (32), alsorotating at the speed of the camshaft, and from that place via theintermediate wheels (8) and (9) and the driven wheel (7) driving thecamwheel (2) to be rotated of the device for the variable control of thevalves. Any exhaust camshaft which may be present is also suitable forthis purpose. FIGS. 9, 10 and 11 show also in this respect differentpossible combinations for the driving of the camshafts by the crankshaftand the arrangement of the adjusting gear in a triple crankshaft engine.In this case, the camshaft (1) not to be rotated can be driven by thecrankshaft (33) by suitable driving means (34), for example, a chain(FIG. 9), or via suitable intermediate drives (35) by the third shaft(32) driving the coupled gear (FIG. 10), or via a common driving means(36) together with the shaft (32) bearing the driving wheel (6) of thecoupled gear (5) (FIG. 11). The camshaft can be driven via suitabledriving means, for example, a toothed belt or chain, by the crankshaftdirect or indirectly via an intermediate shaft. The indirect drive via acentrally disposed intermediate shaft may be of particular advantage,for example, in the case of V-type engines.

Preferably the adjusting mechanism is so arranged that the camshaft (2)to be driven via the coupled gear (5) determines the closure function ofthe or each valve, so that a relative rotation of the camshaft producesa change in the valve closure time. In this way when the device is usedon the intake side, unthrottled load control of 4-stroke engines isrendered possible by the clearly-defined closure of the or each intakevalve at a point in time after the required quantity of charge has beensucked in by the piston. With very low loads this means that the intakevalve is closed prematurely, during the downward movement of the pistonin the intake phase, with correspondingly low maximum strokes. Thisarrangement also permits load control via late closure of the or eachintake valve, during which the excess quantity of charge already suckedin by the piston is again expelled during the subsequent compressionphase. The exhaust side application of the device enables the residualgas component in the fresh mixture to be purposefully controlled bychanging the exhaust closure time.

In addition, by means of the aforementioned device it is also possibleto control in a directed manner the opening time of the or each valve ifthe camshaft (2) driven by the coupled gear (5) determines the openingfunction. In this way on the intake side by controlling in a directedmanner the intake opening time the residual gas content can be adaptedin an optimum manner to the particular operational conditions, and onthe exhaust side expansion work can additionally be utilized, dependingon the operating point.

The geometrical design of the coupled gear determines to an importantextent the sensitivity of the angle of adjustment of the camshaft (2) tobe rotated. The transmission ratios between the driving and drivenwheels and the intermediate wheels and the relative position of thecouplers dependent thereon provide suitable parameters for designing thegear in the optimum manner for the particular application. Theadjustment path of the coupled gear is understood to mean eachexternally initiated change in position of the couplers (10), (11) and(12) which finally adjusts the driven camshaft in relation to thedriving camshaft with a corresponding transmission ratio.

As shown in FIG. 1, the adjustment path and therefore the change inposition can be initiated, for example, as a rotary movement around therigidly casing-attached pivot (P1) of the coupler (10) by means of anadjusting mechanism engaging at point (P5) with a prolongation of thecoupler 10. Adjustment can equally well be initiated on the two othercouplers. For the adjustment itself, various actuators are suitable suchas, for example, hydraulically or pneumatically actuated linearadjusting cylinders or electrically actuated d.c. motors having acorrespondingly adapted transmission. The sensitivity of the angle ofrotation to the change in position initiated in the coupled gear can beinfluenced by the distance between the point of articulation (P5) andthe rigidly casing-attached pivots (P1) and (P2) of the couplers (10)and (12) (a larger distance results in lower sensitivity and viceversa). The value of the resulting angle of rotation is decided not onlyby the adjustment path of the coupled gear, but also by the transmissionratio between the driving wheel (6) and the driven wheel (7) on the onehand and the intermediate wheels (8 and 9) on the other. Thus, anincrease in the operative diameter of the intermediate wheels (8) and(9) in relation to the driving and driven wheels causes an increase inthe angle of rotation of the camshaft (2) to be rotated for the sameadjustment path of the coupled gear; a reduction of the diameter of theintermediate wheels reduces the sensitivity of the camshaft rotation andtherefore of change in the control time. A further parameter isrepresented by the angular position of the couplers in relation to oneanother, which is determined in the last resort by the diameters of thefour gear wheels in contact with one another and the distance betweenthe driving camshaft and the driven camshaft. A crank drive constructedas a parallelogram, produces a linear dependence of the angle ofrotation of the camshaft (2) to be rotated on the initiated adjustmentpath, so that in every position of the coupled gear the angle ofrotation is a constant multiple of the initiated angle of rotationaround the point (P1). When the crank drive deviates from the shape of aparallelogram, a varying degree of non-linear dependence can be achievedbetween the angle of rotation of the camshaft (2) to be rotated and theinitiated change in position. This can be achieved both by differencesin diameter between the intermediate wheels (8) and (9) on the one handand the driving wheel (6) and the driven wheel (7) on the other, andalso by the distance of the pivots (P1) and (P2) from one another. Whileon condition that the two contacting control shafts have the samespeeds, the driving wheel and the driven wheel must in any case haveidentical diameters, the two intermediate wheels can certainly beconstructed with different operative radiuses of engagement.

Very large angles of rotation are permitted with only small initiatedchanges in position, of the coupler (10) by a construction of thecoupled gear, more particularly in the zone of an extended position oftwo adjacent couplers, for example, with an angle between 150° and 180°enclosed by the couplers (11) and (12).

With an overlapping construction of the gear wheels (13) and (14)rigidly connected to the camshaft, according to FIG. 3, the advantagesof a space-saving arrangement of the camshafts close beside one anotherare combined with a reduction of the forces operative on the toothflanks by increasing the size of the gear wheels (13) and (14)associated with the camshafts. For such a construction of the adjustinggear it is moreover advantageous to construct in two parts one of thetwo overlapping gear wheels (13 or 14) and dispose said wheelsymmetrically of the other shaft wheel, so that both the one-part shaftwheel and also the intermediate wheel (15) or (16) associated therewithcan dip into the two-part spur toothed wheel during the adjustmentoperation. In this way undesirable forces perpendicular to the axes ofrotation can be avoided with an overlapping construction.

Due to the alternating forces resulting from the excitations of thevalve drive, in a coupled gear of the construction specified, namely atoothed wheel gear, changes of contact may occur which may finally leadto increased noise excitation (toothed wheel rattle) and even to damageto the pairs of toothed wheels. It may therefore be convenient toprevent such changes of contact by additional steps. In the case ofhelical toothed wheels this can be done by at least one of the toothedwheels being axially divided and clamped in relation to the tooth flanksof the toothed wheel meshing therewith. The clamping can be performed,for example, mechanically by means of springs or else hydraulically.

The adjusting gear can also be clamped, via an additional gear withfrictional connection which connects to one another the drivingcamshaft, and the camshaft to be driven and rotated, via a pair ofwheels having different operative diameters. Such a slight difference indiameter generates a drag force which is superposed on the alternatingforces transmitted by the valve drive and thus, as a resulting pulsatingforce without zero passage, prevents any change of (toothrattle) in thecoupled gear. This additional gear can be constructed either as afriction wheel pairing or as a toothed wheel gear with frictionalconnection. FIG. 4 shows a possible way of clamping the adjusting gearvia a friction wheel pairing. In addition to the drive of the secondcamshaft via the 4-wheel coupled gear, the two shafts (17) and (18) arein contact via two friction wheels (19) and (20) rigidly connectedthereto. The two friction wheels (19) and (20) are constructed withslightly different diameters, the result being a braking or forwardtorque between the driving camshaft and the driven camshaft, thisfinally leading to a clamping of the adjusting gear and preventing achange of contact on the tooth flanks.

FIG. 12 discloses a possible way of generating a forward or brakingtorque via an additional toothed wheel pairing (37) and (38), therebycounteracting a change of contact in the coupled gear. By way ofexample, as shown in FIG. 12, camshaft (1) is driven by the crankshaftvia a wheel (42). Also attached to the camshaft (1) is the driving wheel(6) of the coupled gear, which via intermediate wheels (43) and (44)drives the driven wheel (7) positively connected to camshaft (2) to theother hand. FIG. 12 also shows the two couplers (10) and (12) bearingthe intermediate wheels and also connecting couple (11). The twoadditionally meshing toothed wheels (37) and (38) have slightlydifferent numbers of teeth, thus generating a differential speed asbetween the toothed wheels. Since the toothed wheel (37) is positivelyconnected to camshaft (1), the differential speed must be compensated bya frictional connection to the camshaft (2). In the embodimentillustrated this is done by the toothed wheel (38) being clamped bymeans of a clearly-defined force, for example, by means of a spring(39), which can take the form of a cup spring, against a collar disposedpositively on the camshaft (2), thus rendering possible a relativemovement between the camshaft (2) and the toothed wheel (38) at theplace of contact.

Since by means of the coupled gear only one of the two camshafts of thedevice for the variable control of internal combustion engine valves isphase shifted in relation to the crankshaft, it may be sensible andconvenient to adjust the other camshaft also within sensible limits inrelation to the crankshaft by means of an additional device. Thisoffers, for example, the possibility of changing not only the closuretimes of the or each valve for throttle-free load control, but also theopening control times, thereby suitably adapting the residual proportionof gas in the fresh mixture to the particular operating conditions. FIG.5 shows diagrammatically the adjusting mechanism according to theinvention combined with an additional phase adjuster. The coupler (10)forms part of the coupled gear, which can be adjusted rotatably by anactuator in relation to the frame (27), thus producing a phase shift ofthe second camshaft, which is to be driven. At the same time an axialcam disc (21) is corotated by a positive connection to the coupler (10),for example, via pins (28). The axial cam disc (21) follows matchingaxial surfaces (29) rigidly attached to the frame, the result being anaxial movement of the axial cam disc (21). This movement is transmittedvia contact point (30) to entraining sleeve (22) which is internallyand/or externally helically toothed to opposite hands. The spring (31)secures the non-positive connection at point (30) and urges theentraining sleeve (22) to one end position. The entraining sleeve (22)represents the positive connection between the drive wheels (25) and(26), driven directly or indirectly by the crankshaft, and the camshaft(23) to be driven by the coupled gear. Cooperation of the helicaltoothings between the entraining sleeve (22) and the driving element(24) and also the camshaft (23) produces a relative displacementrotations between the driving element (24), which is rigidly connectedto the driving wheels (25) and (26), and the camshaft (23). The axialcamming function of the axial cam disc (21) and the frame (27) canproduce both forwardly and rearwardly rotating relative adjustments, asrequired, more particularly in respect of the intake opening time inconnection with the intake closing time.

I claim:
 1. Apparatus for variable control of valves in an internalcombustion engine having a crankshaft, said apparatus comprisingfirstand second camshafts having fixed axes and acting on a rocker lever whenin turn acts on a spring loaded valve, gear means for phase-shiftingsaid second camshaft relative to said first camshaft, said gear meanscomprising a driving wheel driving said first camshaft and driven bysaid crankshaft, a first intermediate wheel driven by said drivingwheel, a second intermediate wheel driven by said first intermediatewheel, and a driven wheel driving said second camshaft and driven bysaid second intermediate wheel, said first and second intermediatewheels having moveable axes, whereby moving said axes of saidintermediate wheels phase-shifts said second camshaft relative to saidfirst camshaft, and drag means comprising a pair of engaged wheelshaving different operative diameters mounted on respective first andsecond camshafts, and friction means effective between one of said pairof wheels and one of said camshafts, thereby generating a drag forcewhich is superposed on the force transmitted to the second camshaft bythe driven wheel.
 2. Apparatus as in claim 1 wherein said pair ofengaged wheels are fixed to respective camshafts and havecircumferential surfaces which engage frictionally.
 3. Apparatus as inclaim 1 wherein said pair of engaged wheels are gear wheels havingdifferent numbers of teeth, said friction means being effective betweenone of said engaged wheels and the camshaft to which said one of saidengaged wheels is mounted.
 4. Apparatus as in claim 3 wherein the otherof said engaged wheels is fixed to the camshaft to which the other ofsaid engaged wheels is mounted.
 5. Apparatus as in claim 1 furthercomprisinga first coupling link connecting the axis of the firstintermediate wheel to the axis of the first camshaft, a second couplinglink connecting the axis of the second intermediate wheel to the axis ofthe first intermediate wheel, and a third coupling link connecting theaxis of the second camshaft to the axis of the second intermediatewheel.
 6. Apparatus as in claim 5 wherein said first and third links areparallel in every position of said intermediate wheels.
 7. Apparatus asin claim 1 wherein said driving wheel and said driven wheel are axiallyoffset.
 8. Apparatus as in claim 7 wherein one of said driving wheel andsaid driven wheel is divided into two axially spaced parts which receivethe other of said driving wheel and said driven wheel therebetween. 9.Apparatus as in claim 5 further comprisingan axial cam disc which ismovable axially in response to movement of said first coupling element,an entraining sleeve concentric to said first camshaft and movableaxially in response to movement of said axial cam disc, said sleevehaving internal helical teeth which cooperate with external helicalteeth on said first camshaft and external helical teeth which cooperatewith internal helical teeth on a driving element to which said drivingwheel is fixed.
 10. Apparatus as in claim 1 wherein one of saidcamshafts determines opening movement of said valve and the othercamshaft controls closing movement of said valve.
 11. Apparatus as inclaim 1 wherein said driving wheel is fixed to said first camshaft. 12.Apparatus as in claim 1 wherein said driven wheel is fixed to saidsecond camshaft.